How does Sigma 17-50mm f/2.8 compare to EFS 17-55?

As subject line really. How does the Sigma AF 17-50mm f/2.8 EX DC HSM OS compare to the Canon EF-S 17-55 ?

My problem is that my EF 24-105L is shared between my 7D and my EOS3. Its really best suited to the full frame EOS 3 and its not always wide enough for the 7D. I'm looking to sell my EF-S 10-22 (which doesn't get a lot of use) and buying something in the 17-55 range which can stay on the 7D most of the time, leaving the 24-105 on the EOS 3.

Looking at the reviews on Photozone, the EF-S 17-55 seems a slightly better lens but it costs quite a bit more than the Sigma which isn't a bad lens at all. I suppose I could buy a used copy of the EF-S 17-55 but I'm worried by the USM problems. I understand that the problem has now been addressed on new ones but an older one might fail.

If the EF 17-40L wasn't so...... average, it would be an ideal choice as it would fit on both cameras but the EF-S 17-55 or the Sigma 17-50 can't be used on the EOS 3 which is a shame.

My Sigma on my old 50D was an excellent lens although when thinking back it could always see distortion in images that were taken at the wider end even after corrected in Photoshop. It is sharp. When I tested it on a 7D in the shop I took a snap at 50 mm at 2.8 at 1/15 of a second that looked like it had been taken on a tripod or 1/1000. At least the Sigma has a long warranty which is a great reassurance. I have also had many Sigma's and never had an issue with focusing.

I have only had my 17-50 for about 10 days so far and I must say I am very impressed with it. Of the common grips with it on the Internet, I am not seeing corner softness that the Digital Picture review showed, my lens hood snaps on very securely, and AI servo focusing is as accurate as my USM glass. The one flaw, and it is a pretty big one is the rotating focus ring. I don't have big hands and I still find myself holding the focus ring as it is pretty close to the zoom ring. It's annoying. It's a big flaw, but not a $500 one, so I am still very happy. If I had huge hands, it might be $500 flaw so I do recommend trying one out before buying.

Its a win win situation with either lens. If you want an all Canon set up and don't mind shelling out the extra $$$ then go for it. On the other hand the Sigma is a very well received lens.

Never tried sigma..but I quite don't like sigma matte finish, some have new finish (like 85mm f1.4), the old sigma finish if you don't do it nicely, will "crinke"(is it the rigth word?) Paint...maybe sigma owners can defin what I'm talking about

Have 17-55 almost a year..fast,sharp,and accurate..but It cost more too, and never been issue with dust, USM, and IS (hope so not)

Sigma I think its nice too..have seen photographer with sigma 24-70 with 82mm filter, which is looks "raawr" and intimidating

The sigma is a top notch lens. It has the new finish on it as well.

I love the Sigma 17-50.
It is largely responsible for keeping my 7D safe from eBay, now that the 7D is splitting time with a 5D III.

Thanks for the replies guys. Interesting that only one poster prefers the Canon 17-55. Any other EFS 17-55 owners out there who would like to say why they think the 17-55 is worth the extra cost over the Sigma?

We had the Sigma lens for 10 days, returned it and upgraded to the Canon 17-55 lens. We found that the Canon hit the focus point more often in low light than the Sigma.

The main problem with Sigma lens is finding a good copy. When you find one its very comparable to Canon version. It costs a lot less too. I used 17-55 extensively and recently acquired Sigma as a part of a trade and I should say I am pleasantly surprised with that lens. I am planning to move to 1DIV and I am selling this lens. Otherwise, I don't see a reason to not keep it. It is really good

I found the following review (comparative test of the three fast 17-5x zooms) very helpful when shopping for my fast zoom:

http://darwinwiggett.w​ordpress.com …-and-tamron-17-50mm-f2-8/

It seems to be written in an unbiased way, with neither "pro-Canon" nor "anti-Canon" angles. It admits, for example, the Canon superiority at the edges wide open:

Other highlights (you have to check the test photos yourself):

And in the conclusion:

So Sigma does look to be comparable in overall performance and quality to its Canon counterpart, with a significantly lower price tag. Both lenses are nor perfect; both have weaker and stronger points.

^^^

Thanks for that comprehensive reply. I do have to say that I'm leaning towards the Sigma at the moment.